The present invention pertains to processes for sealing and strengthening water-bearing geological formations by means of water-insensitive polyurethane-resin-forming compositions which comprise a conventional polyisocyanate, a conventional polyol together with a conventional accelerator and a foam stabilizer that is a poly(dimethylsiloxane)-poly(oxyalkylene) block polymer.
In Federal Republic of Germany Pat. No. 1,129,894, a process is described for the sealing and strengthening of geological formations against water or gas with a polyurethane resin which process consists essentially of injecting under pressure into the formation that is to be sealed and strengthened a composition consisting essentially of a mixture of toluene diisocyanate and a polyol containing at least three reactive hydroxyl groups in a liquid carrier.
Polyurethane resins have also been used to strengthen piles of coal and loose mountain formations which have a tendency to collapse, as described in Federal Republic of Germany Pat. Nos. 1,758,185 and 1,784,458. In such processes, a small amount of water is added to the polyol component which produces a foaming of the polyurethane resin after it has been placed in the formation that is to be sealed and strengthened. The foaming is due to the reaction of the water with the isocyanate radicals of the polyisocyanate with the formation of carbon dioxide and urea derivatives.
In order to perform successfully such sealing and strengthening operations, it was necessary that the geological formation be dry. Only after hardening or setting of the liquid resin in the geological formation was sealing or strengthening achieved, after which this presence of water or gas was no longer of consequence or detrimental. It was not possible to seal or strengthen water-bearing fissures or cracks in accordance with heretofore known processes and with the known resin-forming compositions specified for use therein because the isocyanato or carbonylamino group of the polyisocyanate reacted so vigorously to form urea derivatives and evolve carbon dioxide that the major portion of the polyisocyanate was lost before a polyurethane resin could be formed or the pores of the resulting foam were so large that the said foam had insufficient strength.
In reports of actual experiences it was explicitly stated that, in such strengthening and sealing operations with polyurethane resins, water must be kept out of the region of the geological formation that was to be strengthened therewith (see, for example, the article by Ivo Kaiser that was published in Gluckauf, Volume 108, No. 19, pages 865-866).